Design Optimization of X-Bracing using SAP2000

Design Optimization of X-Bracing using SAP2000

Priya Venugopal¹, Revathy Parameshwaran2, Sruthy K. P3, Wilfred James4,

1,2,3,4UG students, Department of Civil Engineering, Mangalam College of Engineering

Ettumannoor, Kottayam

Sankar Bose5 5Assistant Professor,

Department of Civil Engineering, Mangalam College of Engineering, Ettumannoor,

Kottayam

Abstractthis paper focuses on design optimization by studying the performance vs cost relationship of X-bracings using SAP2000 for an open ground storey structure during seismic loading. Bracings are provided to arrest lateral stress and prevent swaying of the given structure. The open ground storey creates a soft storey condition.

KeywordsOpen ground storey; soft storey; bracing; lateral stress, cost.

1. INTRODUCTION

   Steel braced frame is one of the structural systems used to resist earthquake and wind loads in multistoried buildings. Many existing reinforced concrete buildings need retrofit to overcome deficiencies to resist seismic loads. The use of steel bracing systems for strengthening or retrofitting seismically an inadequate reinforced concrete frame is a viable solution for enhancing earthquake resistance. Steel bracing is economical, easy to erect, occupies less space and has the flexibility to design for meeting the required strength and stiffness. Table 2 shows the position of steel bracing.

2. MODELLING

   The building used for analysis is a four-storied RC building with a floor height of 3m as shown fig 1. The building is assumed to be located in a seismic zone V and the earthquake zone is plotted using fig 5. The table 1 provides data regarding the G+3 storey building.

   Table 1. Design data of G+3 storey building

   Sr.No.	Content	Description
   1	No. of Storey	G+3
   2	Floor Height	3m
   3	Material	Concrete(M25) & Reinforcement (Fe415)
   4	Size of Column	C1=300mm×300mm All column of G.F & Outer column
   		C2=280mm×280mm Interior column for Ist & IInd Floor
   		C3=250mm×250mm Interior column for IIIrd floor
   5	Size of Beam	230mm×450mm

   Fig 1: Base model of G+3

   Fig 1 shows a G+3 Storey building with 5 bays in X & Y directions. Fixed restrains are provided at the bottom.

   Table2. Different cases of providing bracing.

   Sr.No.	Designation	Position of bracing
   1	Model 01	Without Bracing
   2	Model 02	Bracing throughout
   3	Model 03	Storey (1+2+3)
   4	Model 04	Storey (2+3)
   5	Model 05	Storey (3)
   6	Model 06	Storey (1+3)
   7	Model 07	Storey (G+2)
   8	Model 08	Alternative direction

   The X-bracings are provided at the exterior parameter of the structure. Soil conditions are considered medium stiff and a damping ratio of 5% and the importance factor taken is 1. The loads are provided as per IS 1893:2002 (Part 1). The structural data is the same for all the structures.

   1. Models considered

      Fig 2: Model 02, 03, 04 & 05

      Fig 3: Model 06 & 07

      Fig 4: Model 08

      • Fig 2, 3 & 4 shows the models of steel bracing provided.

      • In model 08, the bracings are provided for G&2 storey in X-Z plane and for 1 & 3 storey in Y-Z plane.

      • The bracing used in the model is made of steel.

   2. Seismic zone in India

   Fig 5: Major Zonation and Intensity map in India

   Table 3. Region-wise major Earthquakes in India.

   Seismic Region	No. of Earthquakes of Magnitude				Return period
   	5.0-5.9	6.0-6.9	7.0-7.9	8.0+
   Kashmir & Western Himalayas	25	7	2	1	2.5-3 yrs.
   Central Himalayas	68	28	4	1	1 yrs.
   North East India	200	128	15	4	<4 months
   Indo-Gangetic Basin and Rajasthan	14	6	–	–	5 yrs.
   Cambay and Rann of kutch	4	4	1	1	20 yrs.
   Peninsular India	31	10	–	–	2.5-3 yrs.
   Andaman & Nicobar	80	68	1	1	<8 months

   Table 3 provides information regarding the No. of Earthquakes of Magnitude 5.0- 8.0+ & their return period.

3. METHODOLOGY

   In this study 8 models are considered with different bracing combinations as shown in fig 2, 3 & 4. The position combination of X-bracings is entered into the design evaluation of SAP2000. By comparing all the results to the cost parameter the optimal selection of the position of X- bracing is verified. Accodingly, minimum lateral drift is achieved.The procedure is shown in fig 6.

   Bracing type: X-bracing

   Bracing type: X-bracing

   Position: External Parameter

   Position: External Parameter

   Diaplacement in X- direction

   Diaplacement in X- direction

   0.002

   0.0015

   Graph of EQ-x

   M1

   M2 M3

   M4

   M5 M6 M7

   M8

   M1

   M2 M3

   M4

   M5 M6 M7

   M8

   Criteria: Lateral Drift

   Criteria: Lateral Drift

   Without bracing frame

   Design & Analysis

   Compare Compare

   Bracing Cost

   0.001 0.0005

   0

   217 218 219 220

   Joint No:

   Fig 7: Displacement in X-direction vs Joint No:

   Model		Joi	nt No:
   No	217	218	219	220
   M1	0.0008	0.0015	0.0017	0.0017
   M2	0.0006	0.0009	0.001	0.0009
   M3	0.0008	0.0013	0.0015	0.0014
   M4	0.0009	0.0015	0.0017	0.0017
   M5	0.0008	0.0015	0.0018	0.0018
   M6	0.00018	0.0013	0.0015	0.0014
   	0.0006	0.0011	0.0013	0.0012
   M8	0.0008	0.0013	0.0015	0.0014

   Model		Joi	nt No:
   No	217	218	219	220
   M1	0.0008	0.0015	0.0017	0.0017
   M2	0.0006	0.0009	0.001	0.0009
   M3	0.0008	0.0013	0.0015	0.0014
   M4	0.0009	0.0015	0.0017	0.0017
   M5	0.0008	0.0015	0.0018	0.0018
   M6	0.00018	0.0013	0.0015	0.0014
   M7	0.0006	0.0011	0.0013	0.0012
   M8	0.0008	0.0013	0.0015	0.0014

   Table 5. Displacement in Y-direction (EQ-y)

   Optimal Bracings position

   Optimal Bracings position

   Fig 6: Selection of the optimal bracings position

   Fig 6 show how the optimal bracing position is selected by comparing braced frame with G+3 without bracing frame & Bracing cost.

   Table 5 Represents the displacement in Y-direction. The values are given for EQ-y and they are in meters. The values are plotted as graph in fig 8.

4. RESULTS AND DISCUSSIONS

   Model No	Joint No:
   	217	218	219	220
   M1	0.0008	0.0014	0.0016	0.0016
   M2	8.159E-05	0.0002	0.0003	0.0004
   M3	0.0009	0.001	0.0011	0.0011
   M4	0.0008	0.0015	0.0015	0.0016
   M5	0.0008	0.0014	0.0017	0.0017
   M6	0.0009	0.0009	0.0012	0.0012
   M7	7.255E-05	0.0007	0.0008	0.0009
   M8	7.309E-05	0.0007	0.0008	0.0009

   Model No	Joint No:
   	217	218	219	220
   M1	0.0008	0.0014	0.0016	0.0016
   M2	8.159E-05	0.0002	0.0003	0.0004
   M3	0.0009	0.001	0.0011	0.0011
   M4	0.0008	0.0015	0.0015	0.0016
   M5	0.0008	0.0014	0.0017	0.0017
   M6	0.0009	0.0009	0.0012	0.0012
   M7	7.255E-05	0.0007	0.0008	0.0009
   M8	7.309E-05	0.0007	0.0008	0.0009

   Table 4. Displacement in X-direction (EQ-x)

   Displacement in Y-

   direction

   Displacement in Y-

   direction

   0.002

   0.0015

   0.001

   0.0005

   0

   Graph for EQ-y

   M1 M2 M3

   M4

   M5

   M6

   M7

   M8

   M1 M2 M3

   M4

   M5

   M6

   M7

   M8

   217 218 219 220

   Joint No.

   Table 4 Represents the displacement in X-direction. The values are given for EQ-x and they are in meters. The values are plotted as graph in fig 7.

   Fig 8: Displacement in Y-direction vs Joint No.

   • By comparing the above plots, the addition of X- bracing to open ground storey structure improves the performance of the building to some extent.

   • For the nonlinear static analysis, from table 4 it is clear that M2, M7& M8 are producing minimum displacement in X-direction. Fig 7 shows the graphical representation of displacement in X- direction vs joint no. and the models are plotted inside the graph.

   • Table 5 shows that M2, M7 & M8 are producing minimum displacement in Y-direction. Fig 8 shows the graphical representation of displacement in Y-

     direction vs joint no. and the models are plotted inside the graph.

     • By comparing the displacement parameter with cost parameters, we could conclude that M7 and M8 provides better performance than other models. The displacement parameters values are taken from fig 7 & fig 8.

5. CONCLUSIONS

   In this study, the analysis and design software, SAP2000 is utilized to develop a numerical model of G+3 storey structures as shown in fig 1. Standard bracings are provided at the external parameter. From the study, we can conclude that in M2, minimum deflection is obtained which results in lower chances of failure of the structure during an earthquake. Providing bracings throughout the section is not feasible, M7 and M8 can be considered economical and still provide less lateral deflection. The model considered here is symmetrical, Further studies can be carried on unsymmetrical models.

6. REFERENCES

[1]. Shemin T John, Pradeep Sarkar, Deepak Kumar Sahu,Enhancement of the seismic performance of an open ground storeyed building using X-bracings,Journal of IOP Conference series Material Science and Enginerring, Vol.936, pp.757-899 October 2020.

[2]. Bush T. D., Jones E. A. and Jirsa J. O.,, Behaviour of RC frame strengthened using structural steel bracing, Journal of Structural Engineering, Vol.117, No.4, April,1991.

[3]. Marc Badoux and James O. Jirsa,Steel bracing of RC frames for seismic retrofitting, Journal of Structural Engineering, Vol.116, No.1, January 1990.

[4]. IS 1893:2002 Indian Standard Criteria for Earthquake Resistant Design of structures Part1 General Provision and Buildings. (Bureau of Indian Standard: New Delhi)

[5]. Jain S k, Review of Indian seismic code IS 1893(Part1) 2002 Indian Concrete Journal.pp.1414-1422.

[6]. Sujeesh S., Shemi T. John., Enhancement of seismic performance of soft storeyed buildingsInternation Journal of Engineering and Advanced Technology, Vol.7, pp. 152-157, December 2017.

[7]. Sarita Singal, Megha Kalra, Rahul Kalra, Taranjeet Kaur.,Behaviour of RC Framed Building with Different Lateral bracing Systems,Internation Conference in Civil Engineering ,pp. 151-155, August 2012.

[8]. Chiral S Modi, Jasmin A. Gadhiya, Aditya Bhatt Pushover Analysis of a G+3 Storey building with Vertical Irregularity by SAP2000, International Journal of Innovative Science and Research Technology, Vol.2, Issue 5, pp.822-827, May-2017.

[9]. https://nidm.gov.in/images/safety_eq3.jpg

[10]. https://nidm.gov.in/images/safety_eq1.jpg